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UK 59 Build Tutorial 3
    The next step was to machine the areas where the bolt carrier rides
straight and make some filler sections with the internal profile and fit them
up.
       First I welded in the lower filler blocks, removed the section from the
jig and fitted the carrier. Then I welded in the upper fillers and checked the
carrier fit. When both sides were done I cut some .070" fillers for the thin
sections and welded them in.

The first photo shows the center area welded and rough ground. There is
still a small area under the feed tray that needs to be filled. You can see in
the rear the lower and upper fillers have been tacked in and the center
section is ready to be cut with smooth parallel edges for a filler section.

The next photo shows the upper rear filler welded in and partially
machined. The sides need to be machined and the area in front of the
ears needs to be cut to radius.

The next photo shows the rear fillers welded in before machining and
grinding. There are a few more spots that need fillers and welding. The
carrier rides smoothly, the bolt locks up and the rear cap also fits properly.
Here is the receiver with the welding completed and most of the areas
rough ground.